This course provides an overview of the issue of postharvest loss of grains by exploring essential physical, technical, and social dimensions of postharvest supply chains and loss prevention methods globally.
Each year, estimates suggest that 1/3 of all food produced is lost or wasted, making postharvest loss a critical global food security and sustainability issue of today. Key knowledge areas are presented including:
-An overview of postharvest loss
-Supply chain activities such as harvesting, drying, and storage
-Economics and markets
-An introduction to the network of actors working in this field
We face the immense challenge of feeding over 9 billion people by the year 2050. To meet these demands, yields will have to more than double using the same amount of natural resources. In recent years, postharvest loss has been recognized by major institutions including the US government, the United Nations, the CGIAR Research Consortium, and several others as a significant opportunity to impact food security and improve livelihoods. Despite this increased attention, a lack of knowledge, technical capacity, and resources remain obstacles for stakeholders worldwide to act on these issues. This course will, for the first time, provide you as professionals, practitioners, and students, with a comprehensive introduction to postharvest loss processes and begin building capacity for loss prevention worldwide.

Reviews

MS

Very good course , much informative and useful. Thanks to the instructors and coursera.

JQ

Jun 04, 2017

Filled StarFilled StarFilled StarFilled StarFilled Star

Disturbing yet hopeful in that 1/3 pho can be ideally saved. Thanks.

From the lesson

Week 2: Causes: Major Causes & Encounters for PHL

This module will introduce you to technical, social, and economic factors and situations that lead to postharvest losses. Harvesting, drying, and storage phases will be specifically covered as stages that are both vital in the grain supply chain and in which a great deal of postharvest losses are experienced.

Taught By

Dr. Prasanta Kalita

Transcript

Hello, my name is Kent Rausch. I'm on the faculty at the University of Illinois. I work in the Agricultural and Biological Engineering Department. This time we will talk about cleaning methods and equipment for grain and oilseeds. We'll talk about the importance of cleaning, certain cleaning methods, the basic principles and some ideas of equipment that can be used for mechanical cleaning. And talk a little bit about losses on cleaning procedures. Cleaning generally occurs in several places. After the grain has been received and is in storage, it could be cleaned in a preconditioning, or pre-cleaning step. There can also be an additional cleaning step just before it's being processed or bagged and then sent to storage. Cleaning is necessary for several reasons. As the grain has been harvested and handled, there can be foreign materials that are in the grain including dust, chaff, and broken grain and seeds as well as weed seeds. These need to be removed to avoid the occurrence of molds and heat during storage. Weed seeds and other materials can add unwanted flavors and taste to the material when it's being processed and it can also damage processing equipment. This gives a flow chart of what the cleaning equipment is trying to achieve. So following harvest, we'll do a preprocessing step to thresh, shell, or dry the grain. And the inert materials on the left side here, the noxious weeds, deteriorated seed, and so forth, need to be removed from the marketable seed. And also the weed seeds, other crop seeds, other varieties of seed and so forth need to also be removed or may want to be removed. Before we do other steps with the marketable seeds such as cleaning, grading, treating, packaging, and testing. So we can clean the grain before storage, or before processing, or both. Pre-conditioning is a first pass cleaning method. Just removes the larger debris, and leaves, and so on, and so forth. Cleaning is divided into two major categories. One is winnowing, which is largely a manual process. And then screening and sifting. Pre-conditioning or the pre-cleaning step is typically done for mechanized agriculture which can result in stones and leaves and dirt getting into the harvested crop. Pre-conditioning is also used for shelling and debearding operations, so forth. Typical equipment to be used would be a scalper. Huller or scarification equipment, debearding to remove the bristles on various types of grains, a pebble mill and a maize sheller. For winnowing, the general principle is air separation by density. Winnowing recovers the heavier grain and removes things such as chaff. The technology is pretty simple. A manual method may actually use the outside wind velocity or there may be a machine such as a fan or a winnowing machine that blows away the chaff and undesired material. For screening and sifting, we're using separation by size rather than by density. Smaller materials are removed using various size screens. For maize, for example, the screen that would be useful be four and a half millimeters. For grain sorghum or milo, a 2 millimeter sieve, and for rice, 1.4. So this varies depending on the grain that you're trying to clean. The technology can be purely manual, or it can be machine driven. For an air-screen cleaner we're going to combine methods. We're going to use the concepts of size, shape, and density to effect a separation. Typically we may have two air passes or two chances for air to remove lighter material and then two passes for the screens to separate based on size. This slide here shows a typical air-screening cleaner. The grain comes in at the top and is fed in carefully with a hopper. There's an upward flow of air lifting the lighter materials off the screen. The rough scalpings is large material that's undesired. The desired grain is retained on the screen here in the middle of the first pass. Fine material, dirt, and small weed seeds may fall through the screens and are removed. And then there is another pass down below. It's angled so that the oscillations cause the good grain to move downward. And then there is another lifting air passage at the very bottom to lift out more fine materials. This results in clean, graded seed that's fairly uniform in size coming out of this type of a cleaner. This shows another configuration where the air is flowing upwards and the grain is flowing downwards through two passes. The screens are of various sizes depending on the grain and the foreign material that we're trying to remove. The type of screen can vary depending on the grain as well. We can use hardware cloth for scalping off trash and other types of things that might be present in the stored grain, varying from about a half an inch opening down to one eighth inch opening. And then depending on the grain, we may have round, oblong, or lens shaped. Once we've removed the fine materials it may be desired to grade the seeds based on size and shape to create value added, or improved market value for the product. This may be for purposes of seed, or to standardize the grain. We can use the physical characteristics of the grain to grade the material. We can use size or width, length, the shape, whether it's long or oval shaped, color, surface texture and then some electrical properties that we'll touch on. Depending on how the cleaning operation is conducted, there can still be some losses. Generally speaking, manual cleaning results in very low losses. The losses often occur in the machine methods, when the mechanical device hasn't been adjusted properly. The machines can also be improperly sized for the different size of materials that you're trying to separate. And therefore you lose good material with the undesired material that you're trying to remove. Machine losses are also common with improper combine harvesting equipment. And this shows some classic results when using a combine harvester to harvest oil seeds. Some research shows that you have losses of about 5 to 10%, or up to 10%, depending on how the machine is operating. Depending on how you adjust the machine, you can greatly reduce though the grain loss down to nearly zero if you're careful with the operation of the machine. Following harvest, such as at the wheat flour mill, there are several cleaning operations. And this shows a wheat flour mill and the typical methods used to clean the grain before it's milled. This can use the disk separation. We can use gravity separation. There also is metal detectors used before the grain is going to the tempering bins. Where the foreign material can cause problems, can cause improper hydration or milling characteristics downstream as well as damage to the equipment

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